1. Field of the Invention
The present invention generally relates to an apparatus and method for transmitting/receiving data in a multicarrier High-Rate Packet Data (Nx HRPD) system, and more particularly to an apparatus and method for efficiently transmitting/receiving a control channel in a mobile communication system simultaneously supporting a synchronous HRPD system and an Orthogonal Frequency Division Multiplexing (OFDM) system.
2. Description of the Related Art
With the rapid development of communication technologies, mobile communication systems can provide not only the conventional voice service but also a high-rate data service in which large-volume digital data such as E-mails, still images, moving images, and the like can be transmitted to mobile terminals.
Representative examples of current mobile communication systems for providing high-rate data services are EVolution Data Only (EV-DO) and OFDM systems, and the like. To provide a forward transmission rate of about 2.4 Mbps, the EV-DO system has evolved from the conventional Code Division Multiple Access (CDMA) 2000 1× corresponding to one of the high-rate data service standards proposed by Qualcomm, a company in the United States. The EV-DO system is called a High-Rate Packet Data (HRPD) system.
A representative wireless mobile communication system using a multicarrier transmission scheme is an OFDM transmission scheme. The OFDM transmission scheme parallel converts a serially input symbol stream, modulates parallel symbols in multiple subcarriers orthogonal to each other, and transmits the modulated symbols. With the development of Very Large Scale Integration (VLSI) technologies after the early 1990's, OFDM transmission systems have began to come into the spotlight.
Since an OFDM transmission scheme modulates data using multiple subcarriers and maintains orthogonality between the multiple subcarriers, the OFDM transmission scheme is more robust to a frequency selective multipath fading channel as compared with an existing single carrier modulation scheme. The OFDM transmission scheme is suitable for high-rate packet data services such as a broadcast service and the like.
Next, a slot structure and a transmitter structure in a Forward Link (FL) of a conventional HRPD system will be briefly described.
FIG. 1 shows slot structure of the FL in the conventional HRPD system. A half slot is repeated within one slot in which data is transmitted in the FL of the HRPD system. Npilot-chip pilot signals 101 are inserted into the centers of the half slots and are used for channel estimation of the FL in a receiver of a mobile terminal. NMAC-chip Medium Access Control (MAC) signals 102 and 103 including reverse power control information and resource allocation information are transmitted on both sides of the pilot signals 101. NData-chip data 104 and 105 are transmitted on both sides of the MAC signals 102 and 103. The FL slot in the HRPD system is multiplexed in a Time Division Multiplexing (TDM) scheme in which pilot signals, MAC information, data, and the like are transmitted at different times.
On the other hand, the MAC information is multiplexed in a CDMA scheme using Walsh codes. In the FL of the HRPD system, a unit size of each pilot signal block is set to Nplot=96 chips, a unit size of each MAC signal block is set to NMAC=64 chips and a unit size of each data block shown in FIG. 1 is set to NData=400 chips.
FIG. 2 shows a transmitter structure of the FL in the conventional HRPD system. The transmitter is constructed with a channel encoder 201 for channel encoding received packet data, a channel interleaver 202 for interleaving the encoded packet data, and a modulator 203 for modulating the interleaved packet data. Data of a MAC channel passes through a channel encoder 205. A TDM multiplexer (MUX) 206 multiplexes pilot signals, MAC signals and data into a physical link of the slot structure as shown in FIG. 1. Data output from the TDM MUX 206 is transmitted to a mobile terminal through a carrier modulator 207 and an antenna (not shown). In FIG. 2, reference numeral 208 denotes an HRPD compatible processor compatible with a multicarrier HRPD (Nx HRPD) system. The HRPD compatible processor 208 includes the MAC channel encoder 205, the TDM MUX 206 and the carrier modulator 207.
FIG. 3 shows a packet transmission relation between an FL and a Reverse Link (RL) in the conventional HRPD system. Specifically, FIG. 3 shows structures of forward and reverse slots according to reverse packet transmission in legacy Rev. A and B systems. An RL subpacket 300 is included and transmitted in four slots in the legacy system supporting a high-rate packet service.
In terms of the forward slots mapped to the reverse slots, ACKnowledged/Non-ACKnowledged (ACK/NACK) information indicating whether the RL subpacket 300 has been successfully received is allocated to three slots. Also, Power Control Bit (PCB) information for ensuring a channel state of the RL subpacket 300 is allocated and transmitted in one slot.
In other words, in the legacy HRPD Rev. A and B systems, a terminal transmits the RL subpacket 300 to a base station in the four slots. The base station allocates the NACK information indicating when the reception of the RL subpacket 300 has failed or the ACK information indicating when the reception of the RL subpacket 300 has succeeded, to an ACK/NACK field in three slots of the FL. The base station allocates and transmits the PCB information in one slot. The ACK/NACK and PCB information is transmitted in an existing MAC channel.
However, the legacy HRPD Rev. A and B systems may not sufficiently support efficient use of frequency resources and broadband data transmission used by a next-generation system. A scheme for efficiently transmitting control information according to broadband data transmission should be embodied in the next-generation system.